The present invention relates to an iron core retaining structure of an electromagnetic contactor which switches on and off an electric source for an electrical equipment such as a motor.
In most cases, such an electromagnetic contactor has means for absorbing impact force produced when a movable iron core collides against a fixed iron core. FIG. 5 shows an example of a conventional electromagnetic contactor of this type. FIG. 5(a) is a sectional view of the electromagnetic contactor, and FIG. 5(b) is a sectional view of the same electromagnetic contactor in its making state, for explaining the operation of the electromagnetic contactor. In FIG. 5(a), a central leg of an E-shaped fixed iron core 3 is inserted into an exciting coil 5. A movable iron core 4 placed so as to be opposite to the fixed iron core 3 is connected to a movable contact support 6 through a connection plate 7 and supported by a return spring 8. The movable iron core 4 and the fixed iron core 3 are placed in a lower casing 2, with an upper portion of the movable iron core 4 left outside. The bottom portion of the fixed iron core 3 is mounted on a bottom plate of the lower casing 2 through an elastic sheet 13 such as a rubber material. An upper casing 1 defines, by its lower surface 1a, the upward moving distance of the movable contact support 6. A fixed contact 9 attached on the upper surface of the upper casing 1 is made to be opposite to a movable contact 10. The movable contact 10 is attached on the movable contact support 6 so as to be pressed by means of a contact spring 12. Electromagnetic contactor mounting portions 2a are provided on the lower casing 2.
When an exciting coil 5 is energized with an electric current, the fixed and movable iron cores 3 and 4 attract each other so that the movable iron core 4 moves to and collides against the fixed iron core 3. Consequently, as shown in the diagram (b) of FIG. 5, the movable contact 10 comes into contact with the fixed contact 9 to close an electric circuit connected between the fixed and movable contacts 9 and 10. When the current conduction is cut off, the movable iron core 4 is released so as to be moved away from the fixed iron core 3 by the return spring 8, so that the movable contact 10 is separated from the fixed contact 9 to open the electric circuit. When the movable iron core 4 collides against the fixed iron core 3, impact force is caused on the fixed iron core 3 and the movable iron core 4. Thus, the elastic sheet 13 is provided so that the fixed iron core 3 is pressed against the elastic sheet 13 and the elastic sheet 13 absorbs the impact force acting on the fixed iron core 3 because of its flexibility. The impact force acting on the movable iron core 4 is also absorbed when the impact force acting on the fixed iron core 3 is absorbed, whereby the contacts are prevented from chattering.
In the above-mentioned electromagnetic contactor, an elastic sheet such as a rubber material is disposed between the bottom portion of the fixed iron core and the bottom plate of the lower casing in order to absorb impact force due to the collision of the movable iron core against the fixed iron core. The quantity of flexion of the electric sheet is however small, so that the effect of absorption of the impact force is not always sufficient. Furthermore, the impact force acts on the bottom plate of the lower casing on which the electromagnetic contactor mounting portions are provided. Therefore, when the electromagnetic contactor is mounted on a panel, the impact given to the panel and noises are large, so that the adverse affect may be caused on other devices mounted on the panel.